(a) Field of the Invention
The present invention relates to computer network systems in general and more particularly to the management of a multiple-network system.
(b) Prior Art
The use of computer network systems for processing and transmitting data is well known in the prior art. A typical computer network system consists of at least one host computer running under some type of operating system, communication controllers, a communication medium and a plurality of end users (terminals, printers, displays, etc.). The host computer is connected, via a channel, to a first set of the communication controllers. The communication controller interfaces with the communication medium. The communication medium may be telephone lines, satellites, etc. A second set of communication controllers is connected to the communication medium and is connected by one or more device controllers to the end user devices. By entering a request at a user terminal, a user may extract data from the host computer.
In addition to the physical structure, the prior art computing systems are controlled by a system architecture which ensures the orderly flow of information throughout the system. The prior art describes several types of architectures. For example, an overview of the architecture used in computer networks is given in an article entitled, "Computer Network Architecture," by S. Wecker in Computer, September 1979. Another overview, including a description of System Network Architecture (SNA) is given in an article entitled, "An Introduction to Network Architectures and Protocols," by P. E. Green and printed in the IBM System Journal, Vol. 18, No. 2, 1979. In these articles, the various computer networks such as SNA, DMA, ARPANET, etc. are described by means of hierarchical architectural layers, where the lowest layer relates to the physical communication lines interconnecting various user nodes of the network and where the highest level concerns the conversation per se between the various end users of the network.
In an attempt to standardize network architecture, the International Organization for Standardization (ISO) has adopted a model which is described by Herbert Zimmerman in an article entitled, "OSI Reference Model - the ISO Model of Architecture for Open Systems Interconnections," IEEE Transactions on Communications, April 1980. The model architecture consists of seven layers, namely: physical, data link, network, transport, sessions, presentation and application layers. The present invention mainly concerns the session layer which relates to the establishment, termination and control of sessions between two end users.
In order to enable resources in one network to communicate with resources in another network, the prior art utilizes a facility called a gateway for interconnecting the networks. For example, the International Telephone and Telegraph Consultant Committee (CCITT) in an article entitled, "Recommendations X.75 and X.121 of CCITT," 1980 Plenary of the International Telephone and Telegraph Consultant Committee, has defined an interface (X.75) for interconnecting public data network that offers an X.25 user interface. This approach uses a global addressing scheme (X.121) that is apparent at the user interface in each network.
In another prior art approach, the Advance Research Projects Agency (ARPA) interconnects networks using the ARPA-specified virtual call protocol between gateways and routes datagrams from gateway to gateway as local network packets that include a global network address for the destination. A more detailed description of this approach is given in the following articles: C. Sunshine, "Current Trends in Network Computer Network Interconnection," Eurocomp 78; Proceedings of the European Computer Congress, London, England, May 9-12, 1978, On-Line Conference Ltd., Uxbridge, England (1978), pp. 465-472, and F. A. Tobagi, "Multi-Access Protocols in Packet Communication Systems," IEEE Transaction on Communications Com-28, No. 4, 468-488 (April 1980).
Although the above interconnecting gateways work well for their intended purpose, implementation appears to be cumbersome and difficult. It is believed that this drawback stems from the fact that a global address scheme is used. This makes it difficult to use the prior art gateway to interconnect existing independently controlled networks. The use of a global address suggests that all previously assigned addresses have to be redefined to eliminate possible conflicts. As the use of computer networks increases, the desirability for a more efficient approach to interconnect networks will inevitably increase.